RISC-V: Fix MEMREMAP_WB for systems with Svpbmt

RISC-V: Fix MEMREMAP_WB for systems with Svpbmt

Currently, the memremap() called with MEMREMAP_WB maps memory using
the generic ioremap() function which breaks on system with Svpbmt
because memory mapped using _PAGE_IOREMAP page attributes is treated
as strongly-ordered non-cacheable IO memory.

To address this, we implement RISC-V specific arch_memremap_wb()
which maps memory using _PAGE_KERNEL page attributes resulting in
write-back cacheable mapping on systems with Svpbmt.

Fixes: ff689fd21cb1 ("riscv: add RISC-V Svpbmt extension support")
Co-developed-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221114090536.1662624-2-apatel@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>